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  <title>Document</title>
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<body>
  <script>
    /*
    先把所有数字放在一个数组arr里重新组合起来，再过滤掉除了2的子项，计算出数目
    */
    var numberOf2sInRange = function (n) {
      let arr = [];
      for (let i = 0; i <= n; i++) {
        arr.push(i);
      }
      return arr.join("").split("").filter(item => item == 2).length;
    }
    console.log(numberOf2sInRange(25))
  </script>
</body>

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